The present invention relates to an electron gun for a color cathode ray tube (CRT) and, more particularly, to an electron gun for a color CRT producing reduced spherical aberration of electron beams illuminating a screen of the CRT.
Conventionally, an electron gun for a color CRT includes a triode, a plurality of focus electrodes sequentially disposed adjacent to the triode, having electron beam passing holes, and forming an auxiliary lens, and a final accelerating electrode disposed adjacent to the focus electrodes and forming a main lens. Voltages are applied to the triode and the respective electrodes of the conventional color CRT to form a unipotential electron lens and a bipotential electron lens. In order to reduce the spherical aberration of the electron lenses formed between the respective electrodes, reduction of the diameter of the electron beams has been conventionally used.
In order to reduce the diameter of electron beams, as shown in FIG. 1, it has been proposed to enlarge the electron lenses by forming large electron beam passing holes within the neck section of the color CRT, or to enlarge effective electron beam passing holes in each electrode into a single, large electron beam passing hole through which all of three electron beams pass.
The former method requires increased deflection power for a deflection yoke, increasing the power consumption of the CRT. If the diameter of the neck section is reduced to reduce the deflection power needed, the diameters of the electron beam passing holes of the electrodes become smaller. Therefore, as shown in FIG. 2, the electron lens L formed by the electrodes with the reduced area electron beam passing holes has increased spherical aberration. The difference between the focal lengths of an electron beam 1 passing through the center of the electron lens L and an electron beam 2 passing through the periphery of the lens becomes large, thereby enlarging the area of an electron beam spot 3 landing on a fluorescent film of a screen.
The latter method is limited in enlarging the electron beam passing hole because of structural considerations.